In recent years, rapid increase of the Internet has pushed the amount of data transmission sharply, so that high-speed data communications networks have required.
Surface emitting laser elements (or vertical cavity surface emitting laser elements (VCSELs)) are characterized in that laser light can be emitted in a perpendicular direction to the principal surface of a substrate formed with the element and in that the element has low threshold current and high power conversion efficiency. In addition to this, the surface emitting laser elements have various advantages that: they can emit circular light whose cross section perpendicular to the optical axis is circular; two-dimensional arrangement of them is facilitated; and on-wafer inspection of them is carried out easily; other advantages. Moreover, the surface emitting laser elements are expected to be fabricated at low cost. Thus, in the future, the surface emitting laser elements are expected to obtain more increasing demand as light sources for high-speed data communications.
In order to use a surface emitting laser element for a light source for data communications, it is important for the element to have a structure capable of operating at high speed. In order for the surface emitting laser element to accomplish a high-speed operation above 10 Gbit/s in the future, it is especially important to reduce the electrical parasitics such as impedances and capacitance of the light emitting element.
As the electro-optical performance of light-emitting elements continues to be incrementally refined (fine tuned or optimized), electrical parasitic capacitances in these small devices have becoming the critical for the high-speed of operation. As the device speeds increase, electrical parasitics limit the performance of high-speed, the device impedance and pad capacitances are increasingly becomes design factors. This is especially true for all semiconductor electro-optical devices. As the optical qualities continue to be incrementally refined, parasitic capacitances in these already small devices become the criticality in the speed of operation.
For the reasons mentioned above, it is desirable to provide a semiconductor light-emitting element which reduces the parasitic capacitance and therefore improves high frequency performance and modulation speed of light-emitting devices.